High current duoplasmatron having an apertured anode comprising a metal of high magnetic permeability



Nov. 5, 1968 K. L. CHOPRA ET AL HIGH CURRENT DUOPLASMATRON HAVING AN APERTURED ANODE COMPRISING A METAL OF HIGH MAGNETIC PERMEABILITY Filed July 7, 1967 2 Sheets-Sheet 1 To Diffusion Pump INVENTORS KASTURI L. CHOPRA Mi EON RONALD RANDLETT ATTORNEYS United States Patent ABSTRACT OF THE DISCLOSURE A duoplasmatron having an apertured anode of high magnetic permeability which cooperates with magnetic means to focus plasma generated therein. Advantageously the plasma beam is directed on a target causing sputtering onto a substrate. Means are provided for passing a moving web substrate continuously through the sputtered material to receive the sputtered material.

This application is a continuation-in-part of application Ser. No. 579,599, filed Sept. 15, 1966, entitled Duoplasmatron Ion Beam Apparatus, and disclosing apparatus for generating ion beams. The present invention relates in general to a method of developing a well-defined, highcurrent ion beam and in particular to industrial or massproduction sputtering processes utilizing such a beam.

A primary object of the present invention is the improvement of sputtering processes by producing a welldefined ion beam under high vacuum conditions.

A further object of the present invention is to make practical high production industrial processes utilizing duoplasmatrons.

Generally, the present invention consists in methods for producing and utilizing a collimated, high intensity ion beam in a vacuum to remove material rapidly and efiiciently from a target or targets for deposition on a substrate. Alternatively, ions may be precisely and efficiently implanted in a substrate by the same processes. The use of multiple targets for simultaneous or sequential operations to produce films of conducting or nonconducting materials upon a substrate is also made possible. The high rates of deposition permit the metallization of foils or fibers for use in electrical conduction, heat reflection, and various decorative environments. Similarly, alloys or compound coating for magnetic tapes, memory cores, superconducting ribbons, optically transparent resistive coils, semiconductor sheet materials, protective coatings and the like may be sputtered upon substrates because the process is inherently a line-of-sight arrangement due to the welldefined ion beam. Moreover, the high kinetic energy of the atoms of the material being deposited permits reaction and orientation with the substrates at relatively low temperatures. Other applications are possible such as ion implantation, bonding and interconnection of junctions in semiconductor devices, the oxidation of semiconductor materials for masking, the change or control of catalytic surfaces, and the initiation or acceleration of chemical reactions. For a better understanding of the present invention together with other and further objects, features and advantages, reference should be made to the following specification which should be read in conjunction with the appended drawing in which:

FIG. 1 is a schematic sectional view of basic duoplasmatron apparatus suitable for producing the processing beam;

FIG. 2 is a schematic diagram of a production arrangement for vacuum sputtering; and

FIG. 3 shows alternative components for the arrangement of FIG. 2.

As is explained in the above-cited pending application, the duoplasmatron of FIG. 1 includes a cathode 20 disposed in a relatively high pressure region into which a gaseous plasma medium is fed and an anode 40 disposed in a low pressure region. Typically, the chamber in which the cathode is disposed is held at a pressure of about 50 millitorr and the pressure in the lower chamber is maintained at 2 10* torr. The chambers are separated by a base plate 12 in the center of which is mounted an intermediate electrode 36. A nickel aperture of about 3 mm. in diameter is formed centrally of the intermediate electrode.

The water cooled anode 40 is located entirely within the low pressure chamber and it is conical in shape having a central nickel aperture aligned with and of about the same size as that formed in the intermediate electrode. Complete data on the operating voltages and other parameters of the basic duoplasmatron are found in the pending application but, for present purposes, it is sufficient to note that the arc is struck between the cathode and the anode as noted by the legend arc region. The are region encompasses areas in both the high and low pressure chamber. The ion beam is extracted through the aperture of the anode 40 in the low pressure chamber where it is caused to impinge upon the target 56. In the processes of the present invention, it is preferred to locate the substrate 57 at a distance of about 1 inch from the target 56. An ion beam of one-half ampere or more which is well-defined and impinges upon an area of approximately 1 cm. is produced and sputtering rates as great as 10,000 A. per minute has proven attainable.

In FIG. 2, the coating of a continuous web is illustrated. A supply reel 101 of web material 102 is shown in an entrance chamber 103. The entrance chamber 103 is provided with a vacuum sealed door 104 which may be removed to permit the introduction of the reel. The entrance chamber 103 is maintained at a relatively low pressure by the action of a rotary pump (not shown) which is operative to maintain the chamber under continuous vacuum during operation of the system. The reel 101 is mounted upon a freely rotating shaft in any conventional manner. At the opposite end of the illustrated apparatus, is an exit chamber 105 similar in most respects to the entrance chamber 103. Here also, a vacuum sealed door 106 is provided to permit the introduction of a takeup reel 107. Any suitable driving means such as an electric motor may be utilized to rotate the take-up reel about its axis. In this fashion, the web material is drawn from the supply reel through the apparatus to the take-up reel.

Low pressure is maintained in the exit chamber 105 by a rotary pump which may actually be the same rotary pump utilized to maintain the low pressure in the entrance chamber 103.

A suitable opening is provided in a wall of the entrance chamber to permit the web to be drawn from the chamber. The web is drawn through a series of guides mounted for rotation in a transition section attached to the wall of the entrance chamber 103 through which the web 102 passes. As the web 102 passes from the transition section, it enters a first duoplasmatron processing section to which the transition section is attached. The duoplasmatron processing section is generally similar to that shown in FIG. 1. It includes a gas inlet 126, a cathode 120, and an intermediate electrode 136, an associated anode being disposed in a high vacuum region. As in the case of the duoplasmatron of FIG. 1, a relatively low pressure region is maintained about the cathode by a vacuum line 121 and a vacuum is maintained about the anode 140, as explained below. The housing about the Cathode and the intermediate electrode constitute an enclosure into which gas is fed by means of the inlet 126.

The vacuum line 121 leads to a rotary pump system capable of pulling the gas pressure in the cathode area of the duoplasmatron system down to about 50 millitorr. The aperture in the intermediate electrode structure 136 being of only 3 mm. in diameter, maintenance of such a pressure is not difiicult. A plasma is created in the cathode region by the application of appropriate electrical potentials and an ion beam is drawnfrom the plasma by the anode 140 to impinge upon the web material 102. Various details concerning the application of electrical potentials, the cooling of elements, the use of magnetic focusing and the like are identical'to those described in the above-cited pending application. These details have not been illustrated in order to preserve simplicity and easy understanding of the invention.

Duoplasmatron apparatus entirely similar to that described immediately above is disposed beneath the traveling web material 102. In this case, as in the case of the duoplasmatron apparatus disposed above the web material, there is no target utilized, the web material itself constituting the target for the ion beams. Actually, the web is polarized in such a fashion and electrically isolated from the duoplasmatron apparatus to permit it to be bombarded by the ion beams. The effect of the ion bombardment is to heat the web and to degas it to prepare it for further processing operations.

To the left of the duoplasmatron apparatus described above, there is a section to which the high vacuum pumping apparatus is connected. This section includes a plurality of guides 109 to conduct the web on its course. A high vacuum pump, such as a dilfusion pump, is connected to this section through a baffle or cold trap 110. The high vacuum pump, not shown, is capable of pulling the pressure of the high vacuum section down to a pressure of about 2x 10- torr. The high vacuum section not only includes the area in which the guide rolls 109 are disposed, but communicates with the region about the anode 140 and with a large duoplasmatron processing section to be described.

Broadly, the processing section includes multiple duoplasmatron devices each conforming to the embodiment of FIG. 1. In a typical device, there is a cathode region 111 maintained at a gas pressure of about 50 millitorr by means of the gas inlet 112 and the line 113 leading to a rotary pump system (not shown). The cathode region is defined by a housing, a portion of which includes oppositely disposed intermediate electrode structures 114 and 115. Considering the duoplasmatron device at the upper right of the apparatus, there is also an apertured anode 116 and a target electrode 117. The ion beam is drawn through the intermediate electrode 115 and the apertured anode 116 to impinge upon the target 117. Material sputtered from the target 117 impinges upon the section of the web material disposed beneath the target at any given instant. The same sequence of events takes place beneath the web material upon which additional material may be sputtered and further sputtering operations take place above and below the web material after it passes through the guide rollers 118 on its way to the final two duoplasmatron devices. The web material then passes from the duoplasmatron apparatus through a set of guide rolls 119 to the exit chamber 105.

It is not necessary that the web material actually be carried on reels. A vacuum lock 122 may be provided at the entrance chamber 103 into which a continuous web may be introduced as shown in FIG. 3. Similarly, a vacuum lock'may be provided on the exit chamber and the continuous web may then pass from that chamber after processing with no limitations such as might be imposed by the quantity of material that could be wound on a supply reel. Moreover, in some situations, the web 102 may simply act as an endless conveyor belt on which objects to be processed are carried.

The number of processes to which the invention may be applied is almost unlimited. Obviously, sequences and numbers of coatings could be varied and the objects to be coated might equally well receive a single layer by direction of the material from eachtarget upon a'ditferent portion of each object. Directivity may be achieved by suitable tilting of targets and may-be further controlled by the use of magnetic fields.

Because the ion beam which is extracted into the low pressure chambers is well-defined and of high intensity, precise deposition of the sputtered material 'is possible. Moreover, as has been indicated above, the extremely high current of the ion beam makes possible efficient coating of objects at very high speeds. Obviously, the objects to be coated can be of almost infinite variety. As noted, the target materials can be widely varied, there being no need for conductivity of the sputtered material for successful operation. As an alternative to sputtering for coating, the process may be used simply to remove material from the targets. Furthermore, the targets, the web or the objects being carried by the Web may be devices in which it is desired to implant ions. In such case, the ions may be implanted at any desired areas, at any desired depth and in any desired sequence. Of course, the plasma medium may be varied as required to conduct the operations.

Although what has been described constitutes a preferred embodiment of the present invention, it will be recognized by those skilled in the art that the method of extracting a well-defined high intensity ion beam described hereinabove may be utilized in a broad range of applications and environments. The invention, therefore, should not be limited to the details described and shown but only by the spirit and scope of the appended claims.

What is claimed is:

1. In duoplasmatron ion beam apparatus which includes a first chamber adapted to contain a gas at high pressure relative to a second chamber from said first chamber by an intermediate electrode including a portion of high magnetic permeability material through which an apertureis formed communicating between said first and said second chambers, said second chamber containing an anode including a portion of high magnetic permeability material having an aperture therethrough in axial alignment with the aperture in the intermediate electrode, the method which includes the steps of providing said first chamber with a gas at a pressure significantly above pressures which permit sputtering and providing said second chamber with a gas at a pressure which permits sputtering, striking an are extending from the first chamber. through said aperture to the anode in said second chamber, and producing a magnetic field concentrated in the region of both of said apertures for concentrating ions formed by said are into a beam passing through both of said apertures.

2. In the method defined in claim 1, the further step of directing said ion beam passed through said apertures upon a target to sputter material from said target onto a substrate.

3. In the method defined in claim '1, the further steps of maintaining the gas pressure in said first chamber at approximately 50 millitorr and maintainingthe pressure in said second chamber no more than 10 torr.

4. Duoplasmatron processing apparatus comprising, a.

first chamber to which gas is pressure, 7

a second chamber,

supplied at relatively high means for pumping said second chamber down to a rela tively low pressure,

a first aperture is formed, a cathode disposed adjacent one side of said intermediate electrode and within said first chamber, an anode disposed adjacent to the other side of said intermediate electrode and within said second chamber, at least a portion of said anode being formed of a high magnetic permeability material through which a second aperture is formed,

means for applying a moderately high potential of a first polarity between said cathode and said anode and a moderately low potential of said first polarity between said cathode and said intermediate electrode whereby an arc is struck between said anode and said cathode to form a plasma, means for producing a magnetic field in the region of said apertures, said high magnetic permeability portions of said intermediate electrode and said anode concentrating said magnetic field about said apertures, whereby said ion beam is con-fined to a predetermined size and direction,

a target electrode disposed in said second chamber and aligned with said apertures in said intermediate electrode and said anode,

means for directing said ion beam upon said target electrode, whereby material is sputtered from said target, and

means for passing objects through said second chamber in the path of said materials sputtered from said target.

5. Apparatus in accordance with claim 4 including a plurality of chambers corresponding to said first chamber and a plurality of chambers corresponding to said second chamber, each said first chamber including a cathode and each said second chamber including an anode and a target, arcs being struck between each of said cathodes and its associated anode to sputter material from said targets, and

means for passing said objects through said second chambers in predetermined order.

6. Apparatus in accordance with claim 5 wherein said means for passing objects through said second chambers comprises a traveling web upon which said objects are disposed.

7. Apparatus in accordance with claim 6 wherein said web passes from one of said second chambers to another of said second chambers whereby objects disposed upon said web are passed sequentially before one of said targets and another of said targets to form composite coatings of target materials thereon.

8. Apparatus in accordance with claim -5 and further comprising a duoplasmatron heating chamber through which said web is passed, said duoplasmatron heating chamber including a cathode disposed in a first relatively high pressure chamber and an aperture anode disposed in a secondrelatively low pressure chamber,

means for striking an are between said cathode and said anode to form an ion beam and means for directing said ion beam upon said web and objects disposed thereon.

References Cited UNITED STATES PATENTS 2,934,665 4/1960 Ziegler 313-63 3,133,874 5/1964 Morris 204298 3,238,414 3/1966 Kelly et al 313-63 3,315,125 4/1967 Frohlich 31363 FOREIGN PATENTS 1,372,240 8/1964 France.

ROBERT K. MIHALEK, Primary Examiner.

Disclaimer 3,409,529.Kasturi L. Chopra, Lexington, and M ron Ronald Ra'ndlett, North Wllmington, Mass. HIGH CURRENT UOPLASMATRON HAV- ING AN APERTURED ANODE COMPRISING A METAL OF Corporation. Hereby disclaims the terminal portion of the term of said patent subsequent to Oct. 29, 1985.

[Ofiioial Gazette June 3, 1969.] 

